Loose leaf binders typically have two covers that pivot with respect to a binding assembly. Most binders have a spine connecting the covers.
U.S. Pat. No. 3,771,890 teaches a loose-leaf binder formed from a single piece of molded plastic. The binder has only a front and a back cover joined at a flexible portion located at the back of the binder. Each of three split-ring members are mounted to both covers to bias them towards open or closed positions. The covers have curved, directly hinged portions that extend around and are biased by the ring members. Because the covers need to reach completely around the rings, in the open position the shape of the covers lifts papers bound in the rings high above the surface on which the binder is rested when compared to a binder with a spine, which can lay flatter against the surface as the covers are not required to be able to extend completely behind the rings.
Most ring binders, however, have a spine pivotably connected between two covers such that either cover can be opened independently. U.S. Pat. No. 4,295,747, for instance, shows an integrally molded loose-leaf book, in which front and rear cover panels are integrally molded with a spine, and are connected thereto by living hinges. The spine has a rounded contour, and the front and rear cover panels are flat. Thus, when the book laid open on a flat surface in an open position, weight on the cover panels is supported by lateral edges of the cover panels, which rest on the flat surface, and by the living hinges, which are raised above the flat surface by the raised lateral edges of the spine. This can lead to accelerated wear on the hinges, which are already formed as weakened notches.
The ""747 patent also discloses mounting posts that are formed on an inner face of the spine. The posts extend through holes in a matrix strip of a snap-ring assembly. The matrix is secured to the posts with rivets or with fingers of the matrix that bite into the posts.
A binder is thus needed which has a spine that connects two covers, but in which stress is relieved from the hinges where the covers meet the spine.
The invention provides a folder including a spine having a base and first and second spine hinge portions. The spine defines a longitudinal axis and has an exterior surface that is curved around the longitudinal axis. The folder also includes a first cover having a first cover hinge portion pivotably attached to the first spine hinge portion. The first cover has a first curved portion with an exterior surface that is curved around the longitudinal axis. The folder further includes a second cover having a second cover hinge portion pivotably attached to the second spine hinge portion. The second cover has a second curved portion with an exterior surface that is curved around the longitudinal axis. The spine and the first and second curved portions together define a generally rounded contour around the longitudinal axis when the folder is in a closed position.
Preferably, the rounded contour defined by the spine and the first and second curved portions extends along a generally circular or elliptical shape around the longitudinal axis over an angle of approximately 185 degrees.
In one aspect of the invention, the folder is part of a binder having a binding mechanism coupled to the spine and configured for binding a stack of paper. The binding mechanism includes at least two rings. The spine includes a projection that is aligned with one of the two rings when the binding mechanism is coupled to the spine. Preferably, the ring in alignment with the projection lies in a plane transverse to the spine, and the projection is intersected by the plane.